David Cameron has made a historical gaffe in his first visit to the United States as the UK Prime Minister.

Cameron ignited a furious backlash Wednesday when he said that the UK was a 'junior partner' to the US in fighting Nazi Germany in 1940. This is while that the US joined the Second World War a year later in 1941.

The prime minister was accused of forgetting the sacrifices made in 1940 by those who fought in the Battle of Britain, the heroes of Dunkirk and the Londoners bombed out of their homes in the Blitz, Daily Mail reported on Thursday.

As it is historically registered, Britain under the leadership of Winston Churchill stood alone in 1940 against Nazi Germany and had far more forces under arms than the US until 1944.

The US remained neutral until Germany and Japan declared war on it in December 1941 following the attack on Pearl Harbor, but Britain fought on, with some material assistance from the US.

The British military's death toll totaled 449,800 in the war, while the US lost 418,500 of its forces.

The British Prime Minister made the gaffe in an interview with Sky News.

"I think it's important in life to speak as it is, and the fact is that we are a very effective partner of the US, but we are the junior partner," he said. "We were the junior partner in 1940 when we fighting the Nazis".

Even as Downing Street was trying to repair the damage, the PM's error was compounded in a further interview, recorded earlier, with the American network ABC news.

He said: "We were the junior partner in 1940 when we were fighting against Hitler, we are the junior partner now. I think you shouldn't pretend to be something you're not".

General Sir Patrick Cordingley, former commander of the Desert Rats, said: "I am quite sure if Winston Churchill were alive today he would be dismayed".